The present invention relates to a milking apparatus for laboratory animals, and more particularly to a milking apparatus suitable for relatively small and prolific laboratory animals such as, e.g., rats and mice.
Recent years have seen the presence of substances responsible for environmental pollution and harmful to living bodies, such as carcinogenic substances and endocrine disrupting (chemical) substances, becoming a global problem. It is of concern how these harmful substances may affect living bodies through milk such as breast milk. If it becomes possible to collect milk from laboratory animals such as rats and mice by a simpler method, such a method would be a useful means of clarifying the influence of the above-mentioned harmful extrinsic substances on living bodies.
However, relatively small and prolific laboratory animals such as rats and mice have a small nipple and produce only a small amount of milk, and for this reason there has not been proposed an effective milking apparatus. For example, it is difficult to collect milk directly from the nipple of a rat. In laboratories, therefore, milk is usually collected from the stomach of a baby rat that has been fed with milk. In the milk collected from the stomach, however, the milk component may potentially be broken down and digested by having been mixed with saliva and gastric juice and stirred. It is, therefore, an open question whether such milk can be called authentic milk.
C. T. Rodgers proposes (Laboratory Animals (1995) 29, 450-455) an apparatus for directly milking a rat, as shown in FIG. 11. In this apparatus, a milk-collecting test tube 61 is arranged in a glass container 60, which is then closed by a lid 62. One end of a flexible tube 63 is inserted into the milk-collecting test tube 61 in a communicated manner. The flexible tube 63 extends through the lid 62 to the outside of the glass container 60, and its front end is attached to a teat cup 64 made of silicon. The lower part of the glass container 60 is provided with two openings 65, 66, to the latter of which is attached a tube connected to a negative pressure creating source (not shown).
When a rat is milked by using this apparatus, vacuum is drawn from one opening 66 by continuously operating the negative pressure creating source, while the experimenter closes and opens the other opening 65 by a finger to thereby produce a pulsation. The pulsation is transmitted to the teat cup 64 via the flexible tube 63, and milk is collected by the teat cup 64 applied to the nipple of the rat. The above mentioned paper reports that 1.0-1.5 ml of milk was collected, by using the above apparatus, from all the nipples of mother rats on the fourteenth day of lactation.
The above milking apparatus shows that it is possible to directly milk from the nipple of a rat and the apparatus is therefore useful. This milking apparatus, however, requires two experimenters to operate. Namely, one experimenter must put the mother rat in place by one hand and operate the teat cup 64 by the other. The other experimenter must open and close the front end of the pressure-reducing opening 65 with his or her index finger in order to produce a pulsation. Further, since the beat is produced by the finger operation by the experimenter, errors tend to arise due to differences between individual experimenters. Thus, it is not easy to obtain data such as universal milked amount. Moreover, there has been no concrete report about the shape of the teat cup, and this remains an issue to be addressed in the future for better milking.
Accordingly, it is an object of the present invention to provide a novel milking apparatus for laboratory animals by which a single experimenter can perform a milking operation and which makes it possible to obtain milking data universally not influenced by individual differences among experimenters. It is another object of the present invention to provide a novel teat cup particularly suitable for a milking apparatus for laboratory animals.
The present invention provides a milking apparatus for laboratory animals comprising a milk-collecting container whose inside can be kept shut from the outside air, a first and second tubes having one of their ends inserted into an upper part of the milk-collecting container in such a manner as to communicate with the inside of the container, a teat cup replaceably attached to the other end of the first tube, a negative pressure creating source attached to other end of the second tube, and a pressure switching means for switching, in a pulsed manner, the state inside of the second tube between an atmospheric pressure state and a negative pressure state created by the negative pressure creating source.
In this milking apparatus for laboratory animals, the negative pressure creating source is continuously operated, and a negative pressure is developed inside the second tube by connecting it with the negative pressure creating source by means of the pressure switching means. The negative pressure is directly transmitted from the milk-collecting container to the teat cup via the first tube. As the pressure switching means opens the second tube to the atmosphere and the atmospheric pressure develops therein, the teat cup is brought under the atmospheric pressure. Thus, by operating the pressure switching means in a pulsating or cyclical manner, a continuous pulsation develops at the front end of the teat cup.
In that state, the experimenter can perform a required milking operation by putting the mother rat in place with one hand while applying the teat cup to the nipple of the laboratory animal with the other hand. This means that a continuous milking operation can be performed by a single experimenter. This is a great advantage provided by the present invention. Since the repetition of the negative pressure and the atmospheric pressure directly acts on the nipple of the laboratory animal via the teat cup, the milking operation can smoothly proceed even in the case of a small laboratory animal such as a rat.
The milk obtained from the laboratory animal by the pulsation of the teat cup is collected at the lower portion of the milk-collecting container via the first tube. For structural reasons, the milk collected in the milk-collecting container does not flow into the second tube, thereby preventing the pressure switching means and the negative pressure-creating source from being subjected to operational failure.
In the milking apparatus for laboratory animals according to the present invention, the negative pressure creating source may be of any type. In a preferred embodiment, however, a vacuum pump and a pressure controller for controlling the pressure inside the second tube are used as a single unit in constructing the milking apparatus for laboratory animals. By using a negative pressure tank such as an accumulator, a stable pulsation can be obtained. Alternatively, a negative pressure creating means using, as the operating source, the amount of motion of a fluid (such as tap water, air, vapour and the like) flowing at a substantially stable flow rate, such as an aspirator, may be used. In this case, the negative pressure can be easily adjusted to a desired value by adjusting the flow rate of the fluid by opening or closing the tap without using the pressure controller, thereby simplifying the apparatus.
The pressure switching means may comprise an open/close valve such as a two-way electromagnetic valve capable of switching the state inside the second tube between a state where the inside is opened to the atmosphere and a state where the inside is blocked therefrom, with the second tube being connected to the negative pressure source at all times. In another embodiment, the pressure switching means may comprise a first open/close valve for connecting and disconnecting the second tube to and from the negative pressure source and a second open/close valve for switching the state inside the second tube upstream of the first open/close valve between a state where the inside is opened to the atmosphere and another state where the inside is blocked therefrom. In the latter case, too, an open/close valve such as a two-way electromagnetic valve is preferably used. In a further embodiment, an open/close valve of the pulsator valve type conventionally used in cow milking apparatus may be advantageously used.
In the case of using an electromagnetic valve, by providing a computer-controlled control means for controlling the open/close timing of each electromagnetic valve, a stable milking operation can be performed, and this also makes it possible to milk a variety of laboratory animals with the same apparatus under optimum conditions. In addition, in the present invention, the teat cup is adapted to be replaceably mounted on one end of the first tube, so that a teat cup with an optimum shape for a given laboratory animal to be milked can be easily selected and used.
Preferably, the teat cup comprises a top surface portion (liner) having an insertion hole into which the nipple of the laboratory animal is to be inserted, and an outer fitting portion to be fitted with the first tube, the outer fitting portion extending from the periphery of the top surface portion. At least those portions of the top surface portion near the insertion hole are provided with softness and flexibility such that, during milking, they can deform inwardly when a negative pressure develops inside the first tube and return to their original shape when the atmospheric pressure is returned therein.
In the teat cup of this shape, the insertion hole deforms when the top surface portion (i.e., the portion that comes into direct contact with the nipple and udder during milking) deforms inwardly when at negative pressure (milking period), when milk is sucked from the nipple. When at atmospheric pressure (resting period), it returns to its original posture. Such deformation of the top surface portion can provide the same effect as that of stimulating the nipple of the mother by the offspring of the laboratory animals, so that an effective milking operation can proceed.
Experiments show that the above effect can be enhanced by selectively or additionally adopting the features of: making an internal circumferential surface of the insertion hole of the teat cup inclined such that the diameter of the insertion hole becomes smaller towards the first tube with which the teat cup is fitted; forming cuts radially on the teat cup near the insertion hole; and providing a front-end portion of the first tube where the teat cup is mounted with an inclination such that the diameter of the first tube becomes greater towards the teat cup side.
In the experiments conducted by the inventors, in the case of a rat as a laboratory animal, a maximum amount of milk was obtained when a negative pressure of about xe2x88x92210 mmHg, preferably about xe2x88x92150 mmHg, was created at the front end of the teat cup for a predetermined period of time during milking (suction period), though depending on the level of pressure at which the pressure switching means can operate stably. Thus, in the milking apparatus for laboratory animals according to the present invention, preferably a negative pressure in the range of from 0 mmHg to xe2x88x92210 mmHg, preferably from 0 mmHg to xe2x88x92150 mmHg, is created at the front end of the teat cup during milking.